It is well known in the industry to manufacture cartridge cases from either brass or steel. Typically, industry design calls for materials that are strong enough to withstand extreme operating pressures and which can be formed into a cartridge case to hold the bullet, while simultaneously resist rupturing during the firing process.
Conventional ammunition typically includes four basic components, that is, the bullet, the cartridge case holding the bullet therein, a propellant used to push the bullet down the barrel at predetermined velocities, and a primer, which provides the spark needed to ignite the powder which sets the bullet in motion down the barrel.
The cartridge case is typically formed from brass and is configured to hold the bullet therein to create a predetermined resistance, which is known in the industry as bullet pull. The cartridge case is also designed to contain the propellant media as well as the primer.
However, brass is heavy, expensive, and potentially hazardous. For example, the weight of .50 caliber ammunition is about 60 pounds per box (200 cartridges plus links).
The bullet is configured to fit within an open end or mouth of the cartridge case. Certain bullets, mainly for non-military uses, can include a groove (hereinafter referred to as a cannelure) formed in the mid section of the bullet to accept a crimping action imparted to the metallic cartridge case therein. When the crimped portion of the cartridge case holds the bullet by locking into the cannelure or onto the diameter, a bullet pull value is provided representing a predetermined tension at which the cartridge case holds the bullet. The bullet pull value, in effect, assists imparting a regulated pressure and velocity to the bullet when the bullet leaves the cartridge case and travels down the barrel of a gun.
Furthermore, the bullet is typically manufactured from a soft material, such as, for example only, lead. The bullet is accepted into the mouth of the cartridge, and then the cartridge alone is crimped to any portion of the bullet to hold the bullet in place in the cartridge case. Though, typically, the cartridge case is crimped to the cannelure of the bullet.
However, one drawback of this design is that the crimped neck does not release from around the bullet evenly when fired. This is partly due to the fact that the brass casing is not manufactured perfectly. The material thickness around the neck is slightly different causing the case to deform at slightly different rates thus allowing the bullet to be pushed slightly off center when coming out. This leads to uncertain performance from round to round. Pressures can build up unevenly and alter the accuracy of the bullet.
The propellant is typically a solid chemical compound in powder form commonly referred to as smokeless powder. Propellants are selected such that when confined within the cartridge case, the propellant burns at a known and predictably rapid rate to produce the desired expanding gases. As discussed above, the expanding gases of the propellant provide the energy force that launches the bullet from the grasp of the cartridge case and propels the bullet down the barrel of the gun at a known and relatively high velocity.
The primer is the smallest of the four basic components used to form conventional ammunition. As discussed above, primers provide the spark needed to ignite the powder that sets the bullet in motion down the barrel. The primer includes a relatively small metal cup containing a priming mixture, foil paper, and relatively small metal post, commonly referred to as an anvil.
When a firing pin of a gun or firearm strikes a casing of the primer, the anvil is crushed to ignite the priming mixture contained in the metal cup of the primer. Typically, the primer mixture is an explosive lead styphnate blended with non-corrosive fuels and oxidizers which burns through a flash hole formed in the rear area of the cartridge case and ignites the propellant stored in the cartridge case. In addition to igniting the propellant, the primer produces an initial pressure to support the burning propellant and seals the rear of the cartridge case to prevent high-pressure gases from escaping rearward. It should be noted that it is well known in the industry to manufacture primers in several different sizes and from different mixtures, each of which affects ignition differently.
The cartridge case, which is typically metallic, acts as a payload delivery vessel and can have several body shapes and head configurations, depending on the caliber of the ammunition. Despite the different body shapes and head configurations, all cartridge cases have a feature used to guide the cartridge case, with a bullet held therein, into the chamber of the gun or firearm.
The primary objective of the cartridge case is to hold the bullet, primer, and propellant therein until the gun is fired. Upon firing of the gun, the cartridge case seals the chamber to prevent the hot gases from escaping the chamber in a rearward direction and harming the shooter. The empty cartridge case is extracted manually or with the assistance of gas or recoil from the chamber once the gun is fired.
As shown in FIG. 1A, a bottleneck cartridge case 10 has a body 11 formed with a shoulder 12 that tapers into a neck 13 having a mouth at a first end. Note that the shoulder 12 has a uniform thickness, or width. Further, the angle of the shoulder 12 on the outside of the cartridge case 10 is the same as the angle of the shoulder 12 inside the case 10, denoted as α and θ, respectively. In the prior art, α=0, and the shoulder angle α is dictated by the caliber of the cartridge. A primer holding chamber 15 is formed at a second end of the body opposite the first end. A divider 16 separates a main cartridge case holding chamber 17, which contains a propellant, from the primer holding chamber 15, which communicate with each other via a flash hole channel 18 formed in the web area 16. An exterior circumferential region of the rear end of the cartridge case includes an extraction groove 19a and a rim 19b. 
Prior art patents in this area include U.S. Pat. No. 4,147,107 to Ringdal, U.S. Pat. No. 6,845,716 to Husseini et al., U.S. Pat. No. 7,213,519 to Wiley et al., and U.S. Pat. No. 7,610,858 to Chung. The four patents are directed to an ammunition cartridge suitable for rifles or guns and including a cartridge case made of at least a plastics material. However, each has their own drawbacks.
Further, a technical report released in May 2005 by the Armament Research, Development and Engineering Center titled “Alternative Cartridge Case Material and Design” by J. S. Chung, et al. (the “Chung Paper”) describes in detail the failings of certain polymers used in ammunition cartridges and cartridge designs known to the authors. Features and limitations are identified for cartridge, the polymer, and the molding process. Many drawbacks are noted.
Hence a need exists for a polymer casing that can perform as well as or better than the brass alternative. A further improvement are polymer casings that are capable of production in a more conventional and cost effective manner, i.e. by using standard loading presses and better manufacturing techniques.